1. Field of the Invention
The present invention relates to a communication control system, a communication control method, a base station device and a mobile terminal device for carrying out packet communications between the base station device and the mobile terminal device.
2. Description of the Related Art
Conventionally, there are two types of the uplink resource control or traffic control method in the mobile packet communications including a resource reserving type method and a resource non-reserving type method.
Exemplary techniques for this resource reservation includes those disclosed in Japanese Patent Application No. 9-180261 (1997) and Japanese Patent Application Laid Open No. 10-191455 (1998), and these examples use the resource reserving type method for reserving resources according to a reservation from a mobile terminal regardless of types of traffics.
On the other hand, as the resource non-reserving type method, PRMA (Packet Reservation Multiple Access) type access control methods have been proposed. One example of them as disclosed in Japanese Patent Application Laid Open No. 10-136021 (1998) proposes a scheme for controlling the transmission of a reservation request packet by establishing a certain transmission permission as notified from a base station. According to this scheme, when the transmission of the reservation request packet succeeds, the same time-slot of the subsequent frames is also reserved for that mobile terminal, and the time-slot is released after the bursty communications are finished. Also, each mobile station adjusts the transmission permission establishing according to attributes such as its own priority level.
However, the above described resource reserving type method is associated with problems of low resource utilization efficiency including a problem that a reservation delay due to the resource reservation processing occurs for packets in small sizes and a problem that a control overhead becomes large as a rate of reservation signals becomes large. Also, there are cases where the actually used resources are less than the reserved resources due to a variation in the amount of occurred traffics, and in such cases the resources are reserved wastefully so that the resource utilization efficiency is lowered.
Also, the above described resource non-reserving type method has a drawback that the QoS satisfaction level is lowered at the beginning of the burst in the realtime traffic as the quality degradation such as delay or interruption at a time of the start of the burst occurs due to the fact that the transmission of the initial packet is managed by the transmission permission establishing. Also, when there is temporarily no transmission packet during a communication session, the reservation will be released so that there is a possibility of becoming impossible to make the reservation for some time due to a variation of the transmission permission establishing when a next burst occurs, and this situation tends to cause a forceful disconnection of the realtime communication so that it can potentially be a factor for the service quality degradation.